The present disclosure relates generally to industrial power plant machinery and, more particularly, to a method and system for temperature estimation of gas turbine combustion cans.
Gas turbines generally include a compressor and turbine arranged on a rotating shaft(s), and a combustion section between the compressor and turbine. The combustion section burns a mixture of compressed air and liquid and/or gaseous fuel to generate a high-energy combustion gas stream that drives the rotating turbine. The turbine rotationally drives the compressor and provides output power. Industrial gas turbines are often used to provide output power to drive an electrical generator or motor. Other types of gas turbines may be used as aircraft engines, on-site and supplemental power generators, and for other applications.
Certain gas turbines include several tangentially located combustor cans that burn fuel in high-pressure compressed air to isobarically raise the temperature of the resulting gaseous mixture. The resulting hot gas is fed to a multi-stage turbine (known to those skilled in the art as a combination of nozzles and buckets, or stators and rotors in each stage), where the gas performs the work for generating electricity, for example. It is desirable to maintain uniform combustion temperature, and thus, uniform firing temperature for each combustor can. However, variations between individual combustor cans may lead to differences in the firing temperature from each can. Such can-to-can variations adversely affect operability and efficiency of the gas turbine. Because of the extreme high-pressure, high-temperature environment in combustor cans, a direct measurement of the gas temperature is not available, and is therefore indirectly estimated through available measured parameters.
One way of obtaining an estimate of the degree of can-to-can variations is to measure exhaust temperature by using a multitude of tangentially placed thermocouples in the exhaust diffuser, and thereafter monitoring the spread (i.e., the difference between the maximum and minimum temperatures measured by the thermocouples). However, this method is only capable of identifying relatively large can-to-can variations as a result of, for example, a flame blowout in a particular can, and is not sufficient to identify individual hot or cold cans since it does not take into consideration the rotational swirl and mixing effects of the gas as it passes from the combustion cans through the nozzle and bucket stages of the turbine.
On the other hand, swirl maps have also been used to estimate the total rotation (i.e., the swirl of the gas from the cans to the exhaust) and thus map hot spots and cold spots in the exhaust gas, as identified by the exhaust thermocouple measurements to the individual cans. Unfortunately, since the rotation of the gas is not necessarily the same from can to can, as well as from load condition to load condition, the visual interpretation of a swirl map in estimating the gas temperature of individual combustion cans is a difficult proposition. This is especially the case for a turbine having a large number of combustion cans.